This invention relates to an apparatus utilizing microwave to heat-sterilize a sealed container filled with medical fluid and particularly to a microwave oven of coaxial tube type or waveguide type for such purpose.
The sealed container, for example, an ampoule filled with medical fluid such as injection medicine is conventionally subjected to a sterilizing treatment during its manufacturing process.
As means for sterilization, those employing microwave or auto clave are well known.
The means utilizing the microwave is well known, for example, from Japanese Patent Application Disclosure Gazette No. 1973-59976 entitled "Method and apparatus for sterilization of medical fluid contained within ampoule", Japanese Patent Application Disclosure Gazette No. 1973-104381 entitled "Method and apparatus for sterilization of ampoule filled with liquid" and Japanese Patent Application Disclosure Gazette No. 1975-38985 entitled "Sterilizer for ampoule filled with liquid".
The applicant of this application also has already proposed "Apparatus and method for sterilization of sealed container utilizing microwave " in U.S. Pat. No. 5,061,443 and Japanese Patent Application No. 1989-147666 (U.S. patent application Ser. No. 07/530414, U.S. Pat. No. 5,132,504).
The microwave heater of oven type is also well known, for example, from U.S. Pat. No. 4,687,895.
However, it has been difficult for the heating means utilizing the auto clave to control the temperature of individual sealed containers and such heating means sometimes has encountered a problem of medical fluid decomposition. Furthermore, it has been impossible for such heating means to realize a continuous process of manufacturing.
The conventional heating means utilizing the microwave has been inconvenient in that the microwave can not be efficiently absorbed by the sealed container and, to compensate for this, it has been necessary to increase output of the microwave oscillator. In addition, the well known heating means utilizing the microwave has been disadvantageous also in that the sealed container of a large volume can not be adequately sterilized. More specifically, most of such conventional apparatuses have been provided with a single microwave irradiation oven and, therefore, the output of the microwave oscillator for this single oven has had to be increased to heat the sealed container of a large volume. As a result, an extremely intense microwave energy has been concentrated onto the sealed container passing by the oscillator and there has been an anxiety that the temperature of medical fluid could not be controlled.
Specifically, the intense microwave energy is absorbed by the medical fluid contained within the sealed container, leading to a sudden rise of the temperature thereof, and it becomes difficult to control the temperature to a desired level. There have been further problems such as rupture of the container due to a sudden pressure rise within the container and damage of the container due to electric short caused by a high electrolytic intensity of the microwave between the sealed container and the medical fluid contained therewithin.
It has been impossible for the conventional microwave heating apparatus of oven type not only to irradiate a plurality of sealed containers evenly with the microwave but also to achieve a local irradiation and, accordingly, no stable sterilization has been expectable. Particularly in the well known apparatus disclosed by U.S. Pat. No. 4,687,895 which is adapted to convey objects to be heated into respective cavities and to heat them within the respective cavities, there must be provided partition between each pair of adjacent cavities and there must be provided a mechanism used to open and shut these partitions. With a consequence, the mechanical construction is necessarily complicated and heating must be stopped everytime the partitions are opened. Such requirement results in a large heat loss and makes a continuous heating process impossible. The apparatus disclosed by the above-mentioned U.S. Patent has been unpractical for heat-sterilization of ampoule, vial or the like which unexceptionally requires a high accuracy of heat-sterilization, because this apparatus of prior art can not control heating of such object with a desired accuracy.